RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 04 December 2014, 11:00-12:00; Duffield Lecture Theatre

Roland Crocker

"Unravelling the Milky Way's Giant Gamma-Ray and Radio Lobes"

It has been known only since 2010 that the nucleus of the Galaxy launches two giant outflows into north and south Galactic hemispheres. Discovered originally in Fermi gamma-ray telescope data and labelled the ’Fermi Bubbles’, the polarized radio counterparts of these structures were discovered with the Parkes telescope in 2012. The origin of the Bubbles remains enigmatic and controversial with many researchers favouring the idea that they were launched within the last few million years during an active period of the Galaxy’s super-massive black hole. Our theoretical and observational work makes us increasingly confident, however, that the Bubbles were inflated, over much longer timescales, by the intense star-formation occurring around the SMBH. Whatever their origin, the Bubbles represent an up-close-and-personal view of feedback from the nucleus to the Galaxy-at-large. I will present an important, recent discovery we have made about the Bubbles: they contain giant shocks at heights of ~2 kpc above the plane. These shocks reveal themselves as huge linear structures in radio polarization, microwave, gamma-ray, and H-alpha data. The shocks are sites for cosmic ray acceleration. Emission from these cosmic rays explains the ’WMAP Haze’ observed at microwave wavelengths around the Galactic centre as well as the Bubbles’ wider-scale radio polarization and gamma-ray emission. These giant shocks may also be the dominant source of cosmic rays in the Galaxy-as-a-whole above energies of ~10^15 eV.